The preparation of dinitriles, such as adiponitrile (AND), from mononitriloolefins, such as 3-pentenenitrile (3PN) or 4-pentenenitrile (4PN), utilizing zerovalent nickel catalysts has been accomplished with or without a promoter. Likewise, alpha-omega cyanoalkanoates, such as methyl 5-cyanovalerate (5CNV), have been prepared by hydrocyanation of non-conjugated alkenoates, such as methyl 3-pentenoate (M3P) or methyl 4-pentenoate (M4P), using a similar catalyst system. However, the hydrocyanation of the conjugated isomers, such as 2-pentenenitrile (2PN), has not been accomplished and 2PN is reported to be a catalyst inhibitor and yield loss. The process of this invention, i.e., the hydrocyanation of conjugated 2-alkenoates using zero valent nickel catalysts, was therefore unexpected in light of the effect of 2PN, and indeed previously unobserved.
U.S. Pat. No. 2,571,099, issued on Oct. 16, 1951 to Paul Arthur, Jr. et al., discloses the use of nickel carbonyl with or without the addition of a tertiary aryl phosphine or arsine. This process produces a relatively high percentage of undesirable polymeric products when applied to nonconjugated olefinic starting materials and a relatively poor yield in all cases.
U.S. Pat. No. 3,496,215, issued on Feb. 17, 1970 to W. C. Drinkard et al., discloses an improvement in nickel-catalyzed hydrocyanation wherein triarylphosphite ligands are utilized and carbonyl ligands are eliminated, thereby dramatically reducing polymer formation and generally increasing yield to desirable nitrile products.
The teaching of the use of a promoter in the hydrocyanation reaction appears in U.S. Pat. No. 3,496,217, issued on Feb. 17, 1970 to W. C. Drinkard et al. This patent discloses an improvement in hydrocyanation using a promoter selected from a large number of metal cation compounds with a variety of anions as catalyst promoters. The known organometallic compounds (C.sub.2 H.sub.5).sub.3 Al.sub.2 Cl.sub.3 and C.sub.2 H.sub.5 AlCl.sub.2 are also disclosed as promoters.
U.S. Pat. No. 3,496,218, issued on Feb. 17, 1970 to W. C. Drinkard, discloses a nickel hydrocyanation catalyst promoted with various boron-containing compounds, including triphenylboron and alkali metal borohydrides.
U.S. Pat. No. 3,925,445, issued on Dec. 9, 1975 to C. M. King et al., discloses zerovalent nickel hydrocyanation catalysts promoted with metal halides and organoboron compounds.
U.S. Pat. No. 3,852,325, issued on Dec. 3, 1974 to C. M. King, teaches that along with production of 3-pentenenitrile (3PN) in the hydrocyanation of butadiene, there is also obtained varying amounts of cis- and trans-2-pentenenitriles (C-2PN and T-2PN) and that these 2-pentenenitriles are found to be detrimental to catalyst efficiency in the hydrocyanation of 3-pentenenitrile or 4-pentenenitrile (4PN) to adiponitrile (AND).
U.S. Pat. No. 4,774,353 issued on Sept. 27, 1988, discloses a process for the preparation of dinitriles, e.g., AND, from nonconjugated unsaturated nitriles, e.g., 3PN or 4PN, in the presence of a zerovalent nickel catalyst and triorganotin catalyst promoters.
U.S. Pat. No. 4,874,884 issued Oct. 17, 1989, discloses that certain combinations of promoters, e.g., B(C.sub.6 H.sub.5).sub.3 and RAlCl.sub.2, where R is an alkyl group with 1-20 carbons, are synergistic, giving increased rates in the hydrocyanation of 3PN over that expected from either promoter alone.
U.S. Pat. No. 3,865,865 issued on Feb. 11, 1975, discloses the selective removal of 2-pentenenitrile (2PN) from a mixture of alkenyl nitriles. The patent states at column 1, lines 23-25, that "2-pentenenitrile . . . are undesirable byproducts . . . in that they are detrimental to catalyst efficiency." in nickel catalyzed hydrocyanation.
U.S. Pat. No. 3,564,040, issued on Feb. 16, 1971, discloses the removal of trans-2-pentenenitrile from a mixture of pentenenitriles. This patent states that "2PN is both detrimental to catalyst efficiency . . . [and] a yield loss" (Col. 1, lines 55-68), thereby indicating that it cannot be directly hydrocyanated. The nickel catalyzed hydrocyanation of conjugated alkyl 2-alkenoates of the present invention was unexpected in view of the reports that 2PN inhibits hydrocyanation and is a yield loss, i.e., cannot be hydrocyanated.